arXiv subjects

Yuan-Pei Yang

Publications and source records attributed to Yuan-Pei Yang.

89 records · Page 5Linked to original sources

arXiv2019

Relativistic Astronomy. III. test of special relativity via Doppler effect

The "Breakthrough Starshot" program is planning to send transrelativistic probes to travel to nearby stellar systems within decades. Since the probe velocity is designed to be a good fraction of the light speed, \citet{zha18} recently proposed that these transrelativistic probes can be used to study astronomical objects and to test special relativity. In this work, we further propose some methods to test special relativity and constrain photon mass using the Doppler effect with the images and spectral features of astronomical objects as observed in the transrelativistic probes. We introduce more general theories to set up the framework of testing special relativity, including a parametric general Doppler effect and Doppler effect with massive photon. We find that by comparing the spectra of a certain astronomical object, one can test Lorentz invariance and constrain photon mass. Besides, using imaging and spectrograph capabilities of transrelativistic probes, one can test time dilation and constrain photon mass. For a transrelativistic probe with velocity $v\sim0.2c$, aperture $D\sim3.5~{\rm cm}$ and spectral resolution $R\sim100$ (or $1000$), we find that the probe velocity uncertainty can be constrained to $σ_v\sim0.01c$ (or $0.001c$), and the time dilation factor uncertainty can be constrained to $Δγ=|\hatγ-γ|\lesssim0.01$ (or $0.001$), where $\hatγ$ is the time dilation factor and $γ$ is the Lorentz factor. Meanwhile, the photon mass limit is set to $m_γ\lesssim10^{-33}~{\rm g}$, which is slightly lower than the energy of the optical photon.

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arXiv2019

A Search of TESS Full Frame Images for a Simultaneous Optical Counterpart to FRB181228

FRB181228 was detected by the Molonglo Synthesis Radio Telescope (MOST) at a position and time coincident with Transiting Exoplanet Survey Satellite (TESS) observations, representing the first simultaneous multi-wavelength data collection for a Fast Radio Burst (FRB). The large imaged field-of-view of TESS allows a search over the uncertainty region produced by MOST. However, the TESS pixel scale of 21" and the Full Frame Image (FFI) cadence of 30 minutes is not optimal for the detection of an FOB with a possible millisecond duration. We search the TESS FFIs and find no events with a limiting TESS magnitude of 16, assuming a 30 minute event duration, corresponding to an optical flux density upper limit of approximately 2000 Jy for a ~ms signal duration, assuming no signal loss. In addition, the cosmic ray mitigation method for TESS significantly reduces its sensitivity to short timescale transients, which we quantify. We compare our results to the predictions of Yang, Zhang, and Wei (2019) and find that the upper limit is a factor of two thousand higher than the predicted maximum optical flux density. However, we find that if FRB181228 had occurred in the galaxy thought to host the nearest FRB detection to date (37 Mpc), an FOB may have been detectable by TESS. In the near future, when CHIME and ASKAP will detect hundreds to thousands of FRBs, TESS may be able to detect FOBs from those rare bright and nearby FRBs within this large population (if more sophisticated cosmic ray excision can be implemented).

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arXiv2019

How bright are fast optical bursts associated with fast radio bursts?

The origin of fast radio bursts (FRBs) is still unknown. Multi-wavelength observations during or shortly after the FRB phase would be essential to identify the counterpart of an FRB and to constrain its progenitor and environment. In this work, we investigate the brightness of the "fast optical bursts" (FOBs) associated with FRBs and the prospects of detecting them. We investigate several inverse Compton (IC) scattering processes that might produce an FOB, including both the one-zone and two-zone models. We also investigate the extension of the same mechanism of FRB emission to the optical band. We find that a detectable FOB with the current and forthcoming telescopes is possible under the IC scenarios with very special conditions. In particular, the FRB environment would need to invoke a neutron star with an extremely strong magnetic field and an extremely fast spin, or an extremely young supernova remnant (SNR) surrounding the FRB source. Furthermore, most electrons in the source are also required to have a fine-tuned energy distribution such that most of the IC energy is channeled in the optical band. We conclude that the prospect of detecting FOBs associated with FRBs is low. On the other hand, if FOBs are detected from a small fraction of FRBs, these FOBs would reveal extreme physical conditions in the FRB environments.

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arXiv2019

Cosmology-independent estimate of the fraction of baryon mass in the IGM from fast radio burst observations

The excessive dispersion measure (DM) of fast radio bursts (FRBs) has been proposed to be a powerful tool to study intergalactic medium (IGM) and to perform cosmography. One issue is that the fraction of baryons in the IGM, $f_{\rm IGM}$, is not properly constrained. Here we propose a method of estimating $f_{\rm IGM}$ using a putative sample of FRBs with the measurements of both DM and luminosity distance $d_{\rm L}$. The latter can be obtained if the FRB is associated with a distance indicator (e.g. a gamma-ray burst or a gravitational wave event), or the redshift $z$ of the FRB is measured and $d_{\rm L}$ at the corresponding $z$ is available from other distance indicators (e.g. type Ia supernovae) at the same redshift. Since $d_{\rm L}/{\rm DM}$ essentially does not depend on cosmological parameters, our method can determine $f_{\rm IGM}$ independent of cosmological parameters. We parameterize $f_{\rm IGM}$ as a function of redshift and model the DM contribution from a host galaxy as a function of star formation rate. Assuming $f_{\rm IGM}$ has a mild evolution with redshift with a functional form and by means of Monte Carlo simulations, we show that an unbiased and cosmology-independent estimate of the present value of $f_{\rm IGM}$ with a $\sim 12\%$ uncertainty can be obtained with 50 joint measurements of $d_{\rm L}$ and DM. In addition, such a method can also lead to a measurement of the mean value of DM contributed from the local host galaxy.

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arXiv2019

Relativistic Astronomy. II. In-Flight Solution of Motion and Test of Special Relativity Light Aberration

The Breakthrough Starshot project aims to send centimeter-sized, gram-scale "StarChip" probes to Alpha Centauri at a speed of $\sim0.2c$. On the other hand, Zhang \& Li recently proposed that trans-relativistic cameras may be sent to any direction to study astronomical objects and test special relativity. To conduct such "relativistic astronomy", one needs to solve the motion of the probe in flight. We solve the motion of the probe (including the moving direction and the velocity) by comparing the positions of three or more point sources observed in the Earth rest frame and in the probe's comoving frame. When the positions of enough point sources are taken into account, the motion of the probe can be solved with an error which is even smaller than the diffraction limit of the transrelativistic camera. After solving the motion, when the measurement of the position of an additional point source is introduced, one can use the data to test the light aberration effect in special relativity. The upper limit of the photon mass can be placed from the deviation of aberration to slightly lower than the energy of the photon, e.g. $\sim 1 \rm {eV}$.

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arXiv2019

Statistical properties of the repeating fast radio burst source FRB 121102

Currently, FRB 121102 is the only fast radio burst source that was observed to give out bursts repeatedly. It shows a high repeating rate, with more than one hundred bursts being spotted, but with no obvious periodicity in the activities. Thanks to its repetition, the source was well localized with a subarcsecond accuracy, leading to a redshift measurement of about 0.2. FRB 121102 is a unique source that can help us understand the enigmatic nature of fast radio bursts. In this study, we analyze the characteristics of the waiting times between bursts from FRB 121102. It is found that there is a clear bimodal distribution for the waiting times. While most waiting times cluster at several hundred seconds, a small portion of the waiting times are strikingly in the range of 2--40 millisecond. More interestingly, it is found that the waiting time does not correlate with the burst intensity, either for the preceding burst or for the subsequent burst. It strongly indicates that the repeating bursts should be generated by some external mechanisms, but not internal mechanisms. As a result, the models involving collisions between small bodies and neutron stars could be competitive mechanisms for this interesting source.

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arXiv2018

Bunching Coherent Curvature Radiation in Three-Dimensional Magnetic Field Geometry: Application to Pulsars and Fast Radio Bursts

The extremely high brightness temperatures of pulsars and fast radio bursts (FRBs) require their radiation mechanisms to be coherent. Coherent curvature radiation by bunches has been long discussed as the mechanism for radio pulsars and recently for FRBs. Assuming that bunches are already generated in pulsar magnetospheres, we calculate the spectrum of coherent curvature radiation under a three-dimensional magnetic field geometry. Different from previous works assuming parallel trajectories and a mono-energetic energy distribution of electrons, we consider a bunch characterized by its length, curvature radius of the trajectory family, bunch opening angle, and electron energy distribution. We find that the curvature radiation spectra of the bunches are characterized by a multi-segment broken power law, with the break frequencies depending on bunch properties and trajectory configuration. We also emphasize that in a pulsar magnetosphere only the fluctuation of net charges with respect to the background (Goldreich-Julian) outflow can make a contribution to coherent radiation. We apply this model to constrain the observed spectra of pulsars and FRBs. For a typical pulsar ($B_p=10^{12}~{\rm G}$, $P=0.1~{\rm s}$), a small fluctuation of the net charge $δn_{\rm GJ}\sim 0.1 n_{\rm GJ}$ can provide the observable flux. For FRBs, the fluctuating net charge may be larger due to its abrupt nature. For $δn_{\rm GJ}\sim n_{\rm GJ}$, a neutron star with a strong magnetic field and fast rotation is required to power an FRB in the spindown-powered model. The requirement is less stringent in the cosmic comb model thanks to the larger cross section and compressed charge density of the bunch made by the external astrophysical stream that combs the magnetosphere.

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arXiv2018

Synchrotron radiation from electrons with a pitch-angle distribution

In most astrophysical processes involving synchrotron radiation, the pitch-angle distribution of the electrons is assumed to be isotropic. However, if electrons are accelerated anisotropically, e.g, in a relativistic shock wave with an ordered magnetic field or in magnetic reconnection regions, the electron pitch angles might be anisotropic. In this work, we study synchrotron radiation from electrons with a pitch-angle distribution with respect to a large-scale uniform magnetic field. Assuming that the pitch-angle distribution is normal with a scatter of $σ_p$ and that the viewing direction is where the pitch-angle direction peaks, we find that for electrons with a Lorentz factor $γ$, the observed flux satisfies $F_ν\proptoν^{2/3}$ for $ν\llν_{\rm cr}$ ($ν_{\rm cr}$ is the critical frequency of synchrotron), if $σ_p\lesssim1/γ$ is satisfied. On the other hand, if $σ_p\gg1/γ$, the spectrum below $ν_{\rm cr}$ is a broken power law with a break frequency $ν_{\rm br}\sim2ν_{\rm cr}/σ_p^3γ^3$, e.g., $F_ν\proptoν^{2/3}$ for $ν\llν_{\rm br}$ and $F_ν\proptoν^{1/3}$ for $ν_{\rm br}\llν\llν_{\rm cr}$. Thus the ultimate synchrotron line of death is $F_ν\proptoν^{2/3}$. We discuss the application of this theory to blazars and gamma-ray bursts (GRBs).

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arXiv2017

On the synchrotron spectrum of GRB prompt emission

The prompt emission spectrum of Gamma-ray bursts (GRB) is characterized by a smoothly joint broken power-law spectrum known as the Band function. The typical low-energy photon index is $\sim -1$, which poses challenge to the standard synchrotron radiation models. We investigate the electron energy spectrum as a result of the interplay among adiabatic stochastic acceleration (ASA), particle injection, and synchrotron cooling. In the ASA-dominated low-energy range, ASA enables an efficient hardening of the injected energy spectrum to approach a spectral index $-1$. In the synchrotron cooling-dominated high-energy range, the injected high-energy electrons undergo fast synchrotron cooling and have a softer photon spectrum. With the energy range of the injected electrons broadly covering both the ASA- and synchrotron cooling-dominated ranges, the resulting photon number spectrum has the low- and high-energy indices as $α_s \sim -1$ and $β_s \sim -p/2-1$, respectively. The break energy is of the order of $\sim 100 $ keV, depending on the turbulence properties.

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arXiv2017

Dispersion Measure Variation of Repeating Fast Radio Burst Sources

The repeating fast radio burst (FRB) 121102 was recently localized in a dwarf galaxy at a cosmological distance. The dispersion measure (DM) derived for each burst from FRB 121102 so far has not shown significant evolution, even though an apparent increase was recently seen with newly detected VLA bursts. It is expected that more repeating FRB sources may be detected in the future. In this work, we investigate a list of possible astrophysical processes that might cause DM variation of a particular FRB source. The processes include (1) the cosmological scale effects such as Hubble expansion and large-scale structure fluctuations; (2) the FRB local effects such as gas density fluctuation, expansion of a supernova remnant, a pulsar wind nebula, and an HII region; and (3) the propagation effect due to plasma lensing. We find that the DM variations contributed by the large-scale structure are extremely small, and any observable DM variation is likely caused by the plasma local to the FRB source. Besides mechanisms that produce decreasing DM with time, we suggest that an FRB source in an expanding supernova remnant around a nearly neutral ambient medium during the deceleration (Sedov-Taylor and snowplow) phases or in a growing HII region can introduce DM increasing. Some effects (e.g. an FRB source moving in an HII region or plasma lensing) can give either positive or negative DM variations. Future observations of DM variations of FRB 121102 and other repeating FRB sources can bring important clues for the physical origin of these sources.

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arXiv2017

Tight constraint on photon mass from pulsar spindown

Pulsars are magnetized rotating compact objects. They spin down due to magnetic dipole radiation and wind emission. If photon has a nonzero mass, the spin down rate would be smaller than the zero mass case. We show that an upper limit of the photon mass, i.e. $m_γ\lesssim h/Pc^2$, may be placed if a pulsar with period $P$ is observed to spin down. Recently, a white dwarf (WD) --- M dwarf binary, AR Scorpii was discovered to emit pulsed broadband emission with pulses. The spin-down luminosity of the WD can comfortably power the non-thermal radiation from the system. Applying our results to the WD pulsar with $P=117~\rm{s}$, we obtain a stringent upper limit of the photon mass between $m_γ<6.3\times10^{-50}~\rm{g}$ assuming a vacuum dipole spindown, and $m_γ<9.6\times10^{-50}~\rm{g}$ assuming a spindown due to a fully developed pulsar wind.

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arXiv2017

Large host-galaxy dispersion measure of fast radio bursts

Fast radio bursts (FRBs) have excessive dispersion measures (DMs) and an all-sky distribution, which point toward an extragalactic or even a cosmological origin. We develop a method to extract the mean host galaxy DM ($\left\langle{\rm DM_{HG,loc}}\right\rangle$) and the characterized luminosity ($L$) of FRBs using the observed DM-Flux data, based on the assumption of a narrow luminosity distribution. Applying Bayesian inference to the data of 21 FRBs, we derive a relatively large mean host DM, i.e. $\left\langle{\rm DM_{HG,loc}}\right\rangle \sim 270~\rm{pc~cm^{-3}}$ with a large dispersion. A relatively large ${\rm DM_{HG}}$ of FRBs is also supported by the millisecond scattering times of some FRBs and the relatively small redshift $z=0.19273$ of FRB 121102 (which gives ${\rm DM_{HG,loc}} \sim 210 ~\rm{pc~cm^{-3}}$). The large host galaxy DM may be contributed by the ISM or a near-source plasma in the host galaxy. If it is contributed by the ISM, the type of the FRB host galaxies would not be Milky Way (MW)-like, consistent with the detected host of FRB 121102. We also discuss the possibility of having a near-source supernova remnant (SNR), pulsar wind nebula (PWN) or HII region that gives a significant contribution to the observed ${\rm DM_{HG}}$.

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arXiv2016

Testing Einstein's weak equivalence principle with a 0.4-nanosecond giant pulse of the Crab pulsar

Einstein's weak equivalence principle (EEP) can be tested through the arrival time delay between photons with different frequencies. Assuming that the arrival time delay is solely caused by the gravitational potential of the Milky Way, we show that a "nano-shot" giant pulse with a time delay between energies corrected for all known effects, e.g. $Δt<0.4~\rm{ns}$, from the Crab pulsar poses a new upper limit on the deviation from EEP, i.e. $Δγ< (0.6-1.8)\times 10^{-15}$. This result provides the hitherto most stringent constraint on the EEP, improving by at least 2 to 3 orders of magnitude from the previous results based on fast radio bursts.

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arXiv2016

Extracting host galaxy dispersion measure and constraining cosmological parameters using fast radio burst data

The excessive dispersion measures (DMs) and high Galactic latitudes of fast radio bursts (FRBs) hint toward a cosmological origin of these mysterious transients. Methods of using measured DM and redshift $z$ to study cosmology have been proposed, but one needs to assume a certain amount of DM contribution from the host galaxy (DM$_{\rm HG}$) in order to apply those methods. We introduce a slope parameter $β(z) \equiv d \ln \left< {\rm DM}_{\rm E} \right> / d \ln z$ (where DM$_{\rm E}$ is the observed DM subtracting the Galactic contribution), which can be directly measured when a sample of FRBs have $z$ measured. We show that $\left< {\rm DM_{HG}}\right>$ can be roughly inferred from $β$ and the mean values, $\overline{\rm \left }$ and $\bar z$, of the sample. Through Monte Carlo simulations, we show that the mean value of local host galaxy DM, $\left<\rm{DM_{HG,loc}}\right>$, along with other cosmological parameters (mass density $Ω_m$ in the $Λ$CDM model, and the IGM portion of the baryon energy density $Ω_b f_{\rm IGM}$) can be independently measured through MCMC fitting to the data.

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arXiv2016

Fast Radio Bursts from the Inspiral of Double Neutron Stars

In this paper we propose that a fast radio burst (FRB) could originate from the magnetic interaction between double neutron stars (NSs) during their final inspiral within the framework of a unipolar inductor model. In this model, an electromotive force is induced on one NS to accelerate electrons to an ultra-relativistic speed instantaneously. We show that coherent curvature radiation from these electrons moving along magnetic field lines in the magnetosphere of the other NS is responsible for the observed FRB signal, that is, the characteristic emission frequency, luminosity, duration and event rate of FRBs can be well understood. In addition, we discuss several implications of this model, including double-peaked FRBs and possible associations of FRBs with short-duration gamma-ray bursts and gravitational wave events.

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arXiv2016

Synchrotron heating by a fast radio burst in a self-absorbed synchrotron nebula and its observational signature

Fast radio bursts (FRBs) are mysterious transient sources. If extragalactic, as suggested by their relative large dispersion measures, their brightness temperatures must be extremely high. Some FRB models (e.g. young pulsar model, magnetar giant flare model, or supra-massive neutron star collapse model) suggest that they may be associated with a synchrotron nebula. Here we study a synchrotron-heating process by an FRB in a self-absorbed synchrotron nebula. If the FRB frequency is below the synchrotron self-absorption frequency of the nebula, electrons in the nebula would absorb FRB photons, leading to a harder electron spectrum and enhanced self-absorbed synchrotron emission. In the meantime, the FRB flux is absorbed by the nebula electrons. We calculate the spectra of FRB-heated synchrotron nebulae, and show that the nebula spectra would show a significant hump in several decades near the self-absorption frequency. Identifying such a spectral feature would reveal an embedded FRB in a synchrotron nebula.

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arXiv2015

On the polarization properties of magnetar giant flare pulsating tails

Three giant flares have been detected so far from soft gamma-ray repeaters, each characterized by an initial short hard spike and a pulsating tail. The observed pulsating tails are characterized by a duration of $\sim100\,\rm{s}$, an isotropic energy of $\sim 10^{44}\,\rm{erg}$, and a pulse period of a few seconds. The pulsating tail emission likely originates from the residual energy after the intense energy release during the initial spike, which forms a trapped fireball composed of a photon-pair plasma in a closed field line region of the magnetars. Observationally the spectra of pulsating tails can be fitted by the superposition of a thermal component and a power-law component, with the thermal component dominating the emission in the early and late stages of the pulsating tail observations. In this paper, assuming that the trapped fireball is from a closed field line region in the magnetosphere, we calculate the atmosphere structure of the optically-thick trapped fireball and the polarization properties of the trapped fireball. By properly treating the photon propagation in a hot, highly magnetized, electron-positron pair plasma, we tally photons in two modes (O mode and E mode) at a certain observational angle through Monte Carlo simulations. Our results suggest that the polarization degree depends on the viewing angle with respect to the magnetic axis of the magnetar, and can be as high as $Π\simeq30\%$ in the $1-30\,\rm{keV}$ band, and $Π\simeq10\%$ in the $30-100\,\rm{keV}$ band, if the line of sight is perpendicular to the magnetic axis.

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